Mass-spectrometer of double focussing type

ABSTRACT

In a mass-spectrometer of the double focussing type, output ions from an electric field analyzer are applied to a magnetic field analyzer so constructed that the condition indicated by the following equation,

United States Patent 1191 Mitani et al.

111] 3,812,356 May 21, 1974 MASS-SPECTROMETER OF DOUBLE FOCUSSING TYPE [75] Inventors: Eisuke Mitani, Hachioji; Hitoshi Isuyama, Kodaira; Michiyasu ltoh, Kokubunji; Shunroku Taya, Hachioji, all of Japan [73] Assignee: Hitachi, Ltd., Tokyo, Japan [22] Filed: Aug. 23, 1971 [21] Appl. No.: 174,039

[52 US. Cl. 250/419 ME 511 1111. c1. H0lj 39/36 [58] Field of Search 250/419 ME, 41.9 D

[56] References Cited UNITED STATES PATENTS 11/1971 Liebl 250/419 ME OTHER PUBLICATIONS lkegari: Review of Scientific Instruments; Vol. 29;

NO. 11; Nov. 1958; pp. 943-948.

Robinson: Review of Scientific lnstruments;" Vol. 28; No. 10; Oct. 1957; pp. 777-779.

Primary Examiner-Walter Stolwcin Attorney, Agent, or FirmCraig. Antonclli & Hill [57] ABSTRACT In a mass-spectrometer of the double focussing type, output ions from an electric field analyzer are applied to a magnetic field analyzer so constructed that the condition indicated by the following equation.

cose cose sin (,,,'ee) is satisfied therein, where is the deflection angle of the magnetic field analyzer, e is the angle of incidence of the input ions with respect to the magnetic field analyzer and e is the angle of divergence of the output ions focussed at the outside of the magnetic field analyzer.

2 Claims, 2 Drawing Figures ELECTRON 7 MULTIPLIER FATENTEUMAY 21 1974 ELECTRON MULTIFLIER FIG.

PRIOR ART ELECTRON MULTIPLIER FIG. 2

INVENTORS EISUKE MITANI HlTOSHITSUYAMA NICHIYASU ITOH SHUNROKU TAYA BY cmi awtdm H-dlQ ATTORNEYS BACKGROUND OF THE INVENTION This invention relates to the improvement of a massspectrometer of the double focussing type.

As is well known, a conventional mass-spectrometer of the double focussing type developed by Mattauch and Herzog is so constructed that ions having the same velocity and direction can be focussed on the same plane by an electric field analyzer and a magnetic field analyzer so as to attain a desired mass-analysis. Such a device is described, for example, in Mass Spectrometry by R. I. Reed, Academic Press, London and New York, 1965. In this known device, since ions are focussed on the end face of said magnetic field analyzer, when ions are required to be detected electronically, an ion collector is disposed at a position where the ions passing through an orbit having a maximum radius are focussed by scanning the magnetic field.

Therefore, the position of the ion collector is on the end face of said magneticfield analyzer and also a slit disposed in front of the ion collector must be disposed on the end face of said magnetic field analyzer.

However, it is not easy to provide such an arrangement. Moreover, since an ion detector, such as, for example, an electron multiplier, is disposed adajcent to the magnetic field so as to be connected to the output of said ion collector, it is necessary to magnetically shield the ion detector; however, it is difficult to completely attain such magnetic shielding.

Besides, in the case where ions are to be detected by using a photographic plate, this plate must be disposed on the end face of said magnetic field analyzer. Therefore, when it is intended to carry out ion detection by alternately changing the photographic plate and the magnetic field scanning as described above, this changing manipulation and its mechanism become very complicated.

SUMMARY OF THE INVENTION An object of the invention is to provide a massspectrometer wherein the focussing point of the ions is located at the outside of the magnetic field analyzer except the end face thereof.

Another object of the invention is to simplify the changing manipulation and its mechanism in the massspectrometer.

A further object of the invention is to make it easy to arrange an electric detecting means in the magnetic field analyzer.

A still further object of the invention is. to eliminate undesirable influences upon said detecting means due to magnetic field variation.

In order to realize the above objects, a massspectrometer of the invention is so constructed that the condition indicated by the following equation cose cose sin (4% -e e") is satisfied therein, where I m'-is a deflection angle of the magnetic field produced by the magnetic field ana-. lyzer, e is the angle of incidence of the input ions with respect to the magnetic field analyzer and e" is the angle of divergence of the output ions focussed at the outside thereof.

2 BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram showing a conventional mass-spectrometer of the double-focussing type; and

FIG. 2 is a schematic diagram showing an embodiment of the inventon.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Firstly, the principle of a mass-spectrometer of the double focussing type as developed by Mattauch and Herzog will be explained; however, since the construction and operation of said mass-spectrometer are well known, as evidenced by the aforesaid reference and other literature, this description of the known system is limited to the extent required to provide an understanding of the invention.

FIG. 1 shows a basic construction of the abovementioned known mass-spectrometer. In FIG. 1, nu-

As mentioned above, the focal point of the ions is located on the end face AA and the reason for this will be explained by the following. In said massspectrometer, the focal length f,. of the electricfield produced by the electric field analyzer 2, the distance g between the input or output side of said analyzer 2 and its focal point, the focal length f,, of the magnetic field produced by the magnetic field analyzer 3, and the distance g between the input or output side of said analyzer 3 and its focal point are indicated, respectively, by the following equations:

fm m bin) gm m cot 4 where r is the radius of the ion orbit in the electric field produced by the electric field analyzer, q), is the deflection angle of the electric field, r,, is the radius of the ion orbit in the magnetic field produced by the magnetic field analyzer, and 5, is the deflection angle of the magnetic field.

Moreover, in this case, the multiplication factor M of the electric field analyzer and the multiplication factor M,, of the magnetic field analyzer are indicated respectively by the following equations:

e I w n m (fin gm m where 1,, is the distance between a first image point of the ion source 1 (an ion emission point of the ion source 1) and the input side of the electric field analyzer 2, and I,,, is the distance between a second image point focussed by the electric field analyzer and the where A is the distance between both said analyzers and I," is the distance between the output side of the electric field analyzer 2 and the second image point.

The double focussing condition of a conventional mass-spectrometer of the double focussing type'is indicated by the following equation:

When this condition is satisfied, ions having the same velocity and direction can be focussed. At this time, a total multiplication factorM is equal to the product of M, by M i in said mass-spectrometer developed by Mattauch and Herzog, the double focussing condition is satisfied by attaining the following condition: M w M, -*0 10 In order to attain the condition M it is necessary to cause 3,, to be nearly equal to l Namely, the first image point must be positioned at the focal point of the electric field analyzer 2. Consequently, as is apparent from the equation (7), 1 becomes infinite so that the ion beam does not focus at a point between both of the analyzers as mentioned above, and thus, the second image point does not exist therebetween. Moreover, at this time, as is apparent from equation 6, the condition M 0 is satisfied.

Besides, since 3,, becomes nearly equal to 1 is practically determined by the following equation:

m z fe 8e e (l 1) Thus, I,,, can be regarded as having no relation to A, so that it can be selected to be any desired distance. In this case, the deflection angles 4),, and 4) of both said analyzers are determined in such a manner as to satisfy the condition of the equation 10 as follows. The The following equation:

m (jh/fm' 0 is derived from the equations 5, 6, and 9. By subsituting l/M in the equation 8 for this equation 12, the equation 1+ l m v) l (fl' v finH is obtained. In this equation 13, since M,. becomes infinite, and f and f are finite, it can be regarded that the equation is approximately realized. Therefore, the equation vi in im 1 can be derived from the equations 1, 3 and 14, and thus if qb 90, the electric field analyzer must be designed to have the deflection angle 4),, 315l. In this case, as is apparent from equation 4, g,, is zero. That is, the focussing point of ions by the magnetic field analyzer falls on the end face AA thereof, and thus many defects occur as mentioned above.

According to the invention, for the purpose of facilitating a measurement by the magnetic field scanning method, the magnetic field analyzer in the massspectrometer of the double focusing type is so constructed as to cause the focal point of the ions to be located outside of said analyzer, as shown in FlG. 2. By generalizing the equations representing the focal length fm and other factors in the Mattauch Herzog case, the

) following equations are obtained:

thereof, g,,," is the distance between the output side ofthe magnetic field analyzer and the output side focal point thereof, r,,, is the radius of the ion orbit in the magnetic field produced by the magnetic field analyzer when it is operated in accordance with the magnetic scanning method, 1 is the deflection angle of the magnetic fieid in accordance with the magnetic scanning method, 6 is the angle of incidence of the input ions with respect to the normal n, to the input side of the magnetic field analyzer and e is the angle of divergence of the ions with respect to the normal 11 to the output side of the magnetic field analyzer.

Assuming now that ion beam is induced to the input side of the magnetic field analyzer at an angle of namely 5 0, in the same way as the Mattauch Herzog case, the following equation is derived from the equations 1 and 14. In the equation 19, as mentioned above, if =3l5l'. the left side thereof becomes equal to I and thus the following equation cose" sin (q5,,, 6")

is obtained. By substituting cos e" in the equation 18 for the equation 20, the equation 18 is changed into the following equation:

As is apparent from equation 21, the condition m" r,,,' is realized and thus g,,,' does not become substantially zero. Therefore, if, for example, I is set to be 60, r becomes equal to 360 and e and g,,," become about -l and 180,,,,,, respectively. This means that when ions are intended to be detected by means of the magnetic scanning method, as shown in FIG. 2, if the magnetic field analyzer 3 is adjusted to have a deflection angle da of 60, ions induced to the input side of the magnetic field analyzer with the right angle therebetween pass through the orbit having a radius r,,,' 360,,,,,,, and are focussed at a point outside of the magnetic field analyzer with an output angle e of about l5, so that the ion collector 5 can be disposed at the focussed point where g,,,' is 180,,,,,, distant from the magnetic field analyzer. In this case, if the photographic plate method is intended to be employed, the magnetic field analyzer 3 is adjusted to cause the deflection angle 4), thereof to be equal to 90 in the same way as the conventional construction and the photographic plate 4 is disposed on the end face AA of the magnetic field analyzer.

In the above case, the input angle 6' is set to be zero. If e is not zero, the equations and 21 are changed into the following equations:

cos 6 cos 5" sin (4%, e 5'') Therefore, even if e is not zero, g does not become zero. As described above, once the magnetic field analyzer is constituted to obtain the condition indicated by equation 22, the double focussing condition can be attained and at the same time it can be greatly simplified to exchange from the magnetic scanning method into the photographic plate method and vice versa.

What is claimed is:

l. A mass-spectrometer of the double focussing type including an ion source providing ions to be analyzed,

an electric field analyzer supplied said ions to be analyzed and having means producing an electric field 6 for analyzing the ions supplied thereto by means of the electric field,

a magnetic field analyzer disposed so as to be supplied with the ions from the output of the electric field analyzer and having means producing a magnetic field for analyzing the ions supplied thereto by means of the magnetic field, and

a photographic plate disposed on an end face of said magnetic field analyzer so as to allow the ions in said magnetic field analyzer to be focussed onto the photographic plate when said mass-spectrometer is operated in accordance with a photographic plate method,

wherein the improvement comprises:

means for regulating the magnetic field generated in said magnetic field analyzer, when said massspectrometer is operated in a magnetic field scanning method, to focus the ions at a position spaced from the end face of said magnetic field analyzer so as to produce a magnetic field of a magnitude different from that produced when said massspectrometer is operated in accordance with the photographic plate method; and

detector means disposed at said position spaced from the end face of said magnetic field analyzer and outside thereof where the ions are focussed by the magnetic field of the magnitude produced when said mass-spectrometer is operated in the magnetic field scanning method, the mutual disposition of said electric field analyzer, said magnetic field analyzer and said detector means as well as the magnitude of the magnetic field when said massspectrometer is operated in the magnetic field scanning method being defined by the relationship (1),, is the deflection angle by the magnetic field produced by said magnetic field analyzer when said mass-spectrometer is operated in the magnetic field scanning method,

6 is the angle of incidence of ions to be analyzed with respect to said magnetic field analyzer, and

e" is the angle of divergence of analyzed ions with respect to said magnetic field analyzer, whereby said detector means can be less affected by the magnetic field.

2. A mass-spectrometer of the double focussing type capable of being operated in accordance with both photographic plate method and a magnetic field scanning method comprising an ion source providing ions to be analyzed,

an electric field analyzer to which the ions to be analyzed are supplied including means for producing an electric field for analyzing the ions supplied thereto,

a magnetic field analyzer to which the ions derived from said electric field analyzer are supplied including means for producing a magnetic field for analyzing the ions supplied thereto,

a photographic plate disposed on an end face of said magnetic field analyzer and used when said massspectrometer is operated in accordance with the photographic plate method for detecting the analyzed ions, and

an ion detector used when said mass-spectrometer is operated in accordance with the magnetic field scanning method for detecting the analyzed ions,

said magnetic field analyzer including means for regulating said magnetic field producing means, when said mass-spectrometer is operated in the magnetic field scanning method to focus the ions at a position spaced from the end face of said magnetic field analyzer so that the magnetic field has a magnitude different from that produced when said massspectrometer is operated in the photographic plate method, and

said ion detector being disposed at said position spaced from the end face and outside of said magnetic field analyzer so as to satisfy the following equation cos 6' cos e" sin i e e) the magnetic field. 

1. A mass-spectrometer of the double focussing type including an ion source providing ions to be analyzed, an electric field analyzer supplied said ions to be analyzed and having means producing an electric field for analyzing the ions supplied thereto by means of the electric field, a magnetic field analyzer disposed so as to be supplied with the ions from the output of the electric field analyzer and having means producing a magnetic field for analyzing the ions supplied thereto by means of the magnetic field, and a photographic plate disposed on an end face of said magnetic field analyzer so as to allow the ions in said magnetic field analyzer to be focussed onto the photographic plate when said mass-spectrometer is operated in accordance with a photographic plate method, wherein the improvement comprises: means for regulating the magnetic field generated in said magnetic field analyzer, when said mass-spectrometer is operated in a magnetic field scanning method, to focus the ions at a position spaced from the end face of said magnetic field analyzer so as to produce a magnetic field of a magnitude different from that produced when said mass-spectrometer is operated in accordance with the photographic plate method; and detector means disposed at said position spaced from the end face of said magnetic field analyzer and outside thereof where the ions are focussed by the magnetic field of the magnitude produced when said mass-spectrometer is operated in the magnetic field scanning method, the mutual disposition of said electric field analyzer, said magnetic field analyzer and said detector means as well as the magnitude of the magnetic field when said mass-spectrometer is operated in the magnetic field scanning method being defined by the relationship cos Epsilon '' cos Epsilon '''' sin ( phi m'' - Epsilon '' Epsilon '''') where phi m'' is the deflection angle by the magnetic field produced by said magnetic field analyzer when said mass-spectrometer is operated in the magnetic field scanning method, Epsilon '' is the angle of incidence of ions to be analyzed with respect to said magnetic field analyzer, and Epsilon '''' is the angle of divergence of analyzed ions with respect to said magnetic field analyzer, whereby said detector means can be less affected by the magnetic field.
 2. A mass-spectrometer of the double focussing type capable of being operated in accordance with both photographic plate method and a magnetic field scanning method comprising an ion source providing ions to be analyzed, an electric field analyzer to which the ions to be analyzed are supplied including means for producing an electric field for analyzing the ions supplied thereto, a magnetic field analyzer to which the ions derived from said electric field analyzer are supplied including means for producing a magnetic field for analyzing the ions supplied thereto, a photographic plate disposed on an end face of said magnetic field analyzer and used when said mass-spectrometer is operated in accordance with the photographic plate method for detecting the analyzed ions, and an ion detector used when said mass-spectrometer is operated in accordance wiTh the magnetic field scanning method for detecting the analyzed ions, said magnetic field analyzer including means for regulating said magnetic field producing means, when said mass-spectrometer is operated in the magnetic field scanning method to focus the ions at a position spaced from the end face of said magnetic field analyzer so that the magnetic field has a magnitude different from that produced when said mass-spectrometer is operated in the photographic plate method, and said ion detector being disposed at said position spaced from the end face and outside of said magnetic field analyzer so as to satisfy the following equation cos epsilon '' cos epsilon '''' sin ( phi m'' - epsilon '' -epsilon '''') where phi m'' is the deflection angle by the magnetic field of the magnitude produced when said mass-spectrometer is operated in the magnetic field scanning method, epsilon '' is the angle of incidence of ions input from said electric field analyzer with respect to said magnetic field analyzer, and epsilon '''' is the angle of divergence of the ions output from said magnetic field analyzer with respect thereto, whereby said ion detector can be less affected by the magnetic field. 